The invention relates to improvements in machines wherein single-layer or multiple-layer webs or sheets of textile material, paper, metallic foil, plastic foil or the like are treated during travel through the nips of rolls. Typical examples of such machines are printing, punching or stamping machines wherein webs of paper or other material are caused to advance through the nip or nips of one or more pairs of rolls which rotate in opposite directions.
The pressure which the rolls of a stamping, printing, punching or like machine apply to a running web of paper or the like must be regulated with a high degree of precision. The arrangement is normally such that the pressure should remain constant at all times, even in response to changes of load. Furthermore, it is desirable and advantageous to mount the rolls in such a way that they can be readily moved apart in order to introduce the leader of a web into the nip of such rolls, and that the rolls can be readily and rapidly moved to operative positions in which they bear upon the running web with a prescribed optimum force.
As a rule, the rolls in a stamping, punching or like machine carry pairs of so-called Schmitz rings which are bearing rings made of hardened metallic material and provided with cylindrical peripheral surfaces. The peripheral surfaces of bearing rings on one of the rolls abut the peripheral surfaces of bearing rings on the other roll to thus ensure that the distance between the axes of the rolls remains at a selected value. A drawback of such bearing rings is that the distance between the axes of the rolls cannot be reduced, i.e., the radial distance of the axes of the rolls from one another cannot be reduced when the cylindrical peripheral surfaces of bearing rings for one of the rolls abut the cylindrical peripheral surfaces of bearing rings for the other roll. On the other hand, radial adjustability of the rolls relative to each other is desirable, advantageous and often indispensable in order to compensate for changes of dimensions as a result of heating or cooling of the rolls and their bearing rings, to compensate for wear upon the bearing rings and/or upon the rolls, and/or to account for changes of the thickness of running webs or sheets.
Conformance of the width of the nip of two rolls to the thickness of a conveyed web, such as a paper web, is particularly important in connection with rotative stamping or punching of adhesive-coated labels. Thus, it is necessary to invariably cut through the layer which is to be converted into a series of labels but to leave the substrate (to which the labels adhere) intact. Such machines can operate properly, and their output can be satisfactory, only if they are provided with means for permitting repeated adjustment of the width of the nip of the rolls while the machines are in actual use. Even minor manufacturing tolerances and/or minor wear upon the rolls will necessitate highly accurate adjustments in order to ensure that each label will be fully separated from the remnent of the respective layer of the laminated structure which is caused to pass through the nip while the substrate remains intact.
German Offenlegungsschrift No. 31 31 167 discloses a Schmitz ring which is adjustable, i.e., which is designed with a view to change its diameter. This is achieved by furnishing the Schmitz ring with replaceable bands or hoops which are made of sheet steel and are separably connectable to a rim of the Schmitz ring. Each hoop has a different thickness. A drawback of such proposal is that the diameter of the Schmitz ring can be changed only while the machine in which the ring is used is at a standstill. Moreover, it is necessary to move the roll which is provided with such Schmitz rings away from the neighboring roll or rolls so as to provide ample room for removal of previously used hoops and for the application of freshly selected hoops. Each exchange of hoops takes up a considerable amount of time. Still further, each Schmitz ring must be furnished with a large number of spare hoops, especially if it is desired to bring about numerous minimal changes of the outer diameter of the ring.
German Offenlegungsschrift No. 22 05 527 proposes to replace Schmitz rings with races and to employ a further (rolling) ring which operates between a pair of races. Two races must be freely rotatable about the axis of one of the rolls. A drawback of this proposal is the high cost and that the operation of the machine wherein the rolls are held at a desired axial distance from each other is satisfactory only as long as the bearings do not run out of true.